The man objective of this study is to establish the suitability of feline T-lymphotropic lentivirus (FTLV) infection as an animal model for human immunodeficiency virus (HIV) infection of man. If found to be suitable, the cat system would provide a cheap and accessible model for HIV infection that could be used by AIDS researchers with limited resources or no access to non-human primates or human subjects. It would be possible using cats to rapidly and economically screen a large number of drug or vaccine preparations for safety and efficacy in a in vivo system closely resembling human AIDS. Preliminary screening in cats would identify the most promising preparations, which could be screened in-turn in primates. The cat model would hopefully allow AIDS researchers to conserve valuable and limited primate resources for only the most promising treatment or vaccination regimens. Studies of FTLV infection of cats will be directly at 6 major areas: 1) seroepidemiologic studies to define the geographic range and incidence of the infection in nature and the spectrum of disease syndromes it causes, 2) studies involving experimentally and naturally FTLV infected cats to define essential similarities or differences in the pathogenesis of the infection in cats compared to man, 3) development of reagents essential for the study of the infection by laboratory investigators, e.g., characterized stocks of infectious virus, accurate antibody and antigen detection tests, monoclonal antibodies to viral structural proteins and to lymphocytes subset markers, 4) pathological studies, 5) studies comparing the immunologic aspects of the feline disease with HIV infection of man, and 6) antigenic and genetic comparison of FTLV with other known lentiviruses of animals and HIV. These latter studies would be concerned with the creation of genetic probes, full-length infectious DNA clones of virus, and amino sequencing of the entire genome.